patch 9.1.1056: Vim doesn't highlight to be inserted text when completing

Problem:  Vim doesn't highlight to be inserted text when completing
Solution: Add support for the "preinsert" 'completeopt' value
          (glepnir)

Support automatically inserting the currently selected candidate word
that does not belong to the latter part of the leader.

fixes: #3433
closes: #16403

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index e2243f6..87c6039 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -41625,7 +41625,9 @@
   the "matches" key
 - |v:stacktrace| The stack trace of the exception most recently caught and
   not finished
-- New option value "nosort" for 'completeopt'
+- New option value for 'completeopt':
+	"nosort"	- do not sort completion results
+	"preinsert"	- highlight to be inserted values
 - add |dist#vim9#Launch()| and |dist#vim9#Open()| to the |vim-script-library|
   and decouple it from |netrw|
 - 'termguicolors' is automatically enabled if the terminal supports the RGB